The present invention relates to a liquid displacement apparatus and a liquid displacement method.
FIG. 1 is an explanatory diagram showing a constitution of a flushing apparatus of direct displacement type (or full-flow type). FIG. 1 shows a semiconductor wafer 1, a processing tank 2, a supply line 3 for supplying liquid (pure water or chemical solution) to the processing tank 2 through a supply nozzle 4, and a drain 5. In this flushing apparatus, when flushing semiconductor wafers, various liquids are displaced while always overflowing pure water except for a certain standing process time.
The liquids are displaced as follows.
Pure water and liquid are supplied into, for example, a mixing valve (not shown) connected to the supply line 3.
Consumption of pure water at this time is huge, for example, supposing one-hour flushing process in the condition of pure water of 20 liters/min, one processing tank requires more than 1 m.sup.3 of pure water. Huge consumption of pure water means huge drainage, and it has significant effects on the wastewater treating system of the plant, and problems are serious. In addition, it is predicted that 300 mm wafers be used in next-generation devices, and the required capacity of processing tank is about two times larger, and problems are more serious about consumption of pure water and treatment of wastewater.
In a conventional apparatus constitution, first, to supply pure water, a pure water supply valve is opened to supply pure water, and then a liquid supply valve is opened to supply liquid. When supply of liquid is over, the liquid supply valve is closed to stop supply of liquid, while pure water is supplied continuously until the liquid concentration becomes lower than a specific standard in order to drain the residual liquid (this is called "rinse process"). The rinse time required for displacing liquid with pure water is considerably long for the entire flushing process time, and more than half of the entire flushing time is occupied by the rinse time for drainage of liquid by pure water, and this rinse process is bottleneck for shortening the time and simplifying the entire flushing process. This rinse time is so long because, in stationary convection, multiple tiny whirls are formed around the semiconductor wafer 1, and the displacement efficiency of liquid and pure water is lowered by the whirls.
It is thus a problem of the conventional apparatus that, as the consumption of pure water is enormous, it takes a longer time in the rinse process for displacing the liquid with pure water.